1. Field of the Invention
The present invention relates to improvements in a grinding machine to grind to a specific shape the end portion of welding electrodes of tungsten, molybdenum, chromium and the like for use in such welding techniques as TIG welding and plasma arc welding.
2. Description of the Prior Art
The shape of the end portion of a welding electrode for use in TIG welding is dependent on factors such as electric current density, current distribution and cooling effects etc. in the welding area and affects the efficiency of welding work and the welding quality. Therefore, the end portion of the welding electrode is finished to a proper shape, for example, a sharp cone or two-step cut formed of a tapered area and a flat area (a so-called xe2x80x9ctruncated conic shapexe2x80x9d) depending, on the material and thickness of the base metal, welding conditions and other factors. The external surface of the tip of the welding electrode finished to a specific form is polished to a high degree of smoothness. Tungsten electrode A for TIG welding as shown in FIG. 12, for example, has a diameter D of 0.5 to 2.0 mm and tapers to a hemispherical tip A0 with a radius (R) of 0.08 to 0.1 mm. It is desirable that the external surface of the hemispherical tip A0 is more smoothly ground than the tapered section A1 of the electrode. If the external surface of the hemispherical tip A0 is finished to a mirror surface or a specular surface, the directivity and stability of the arc will be substantially improved.
To this end the end portion of the electrode A is usually ground by a special electrode grinding machine. Such as the machine shown in FIG. 13 and disclosed in unexamined Japanese utility model application No. 4-60386 and unexamined Japanese patent application No. 7-276211. The following two methods are widely adopted. In a first method (hereinafter referred to as xe2x80x9cthe first methodxe2x80x9d), a grinding disk B1 which has a relatively large grain size (#170, for example) is fixed on motor drive shaft M1 is used to grind the end portion of electrode A to a specific form. Then, the grinding disk B1 is replaced with a grinding disk B2 which has a finer grain size (#500, for example). By use of the grinding disk B2, the tip of the electrode is finely ground. In a second method (hereinafter referred to as xe2x80x9cthe second methodxe2x80x9d), two grinding machines are used. One is equipped with grinding disk B1 which has a large grain size and another with grinding disk B2 which has a fine grain size. The end portion of the electrode is shaped to a specific form with the grinding disk B1, and is then finely ground or polished with the grinding disk B2.
In FIG. 13, the letter C indicates a housing, the letter M a grinder motor, the letter D a grinding disk clamping screw, the letter E a dust cover, and the letter F an electrode guide.
However, the problem with the first method is that two grinding disks B1, B2 have to be changed for each stage of the grinding work and therefore the grinding process is inefficient and slow.
The second method requires two electrode grinding machines, which represents poor economy and results in increased maintenance costs.
Furthermore, the axial position of electrode A is often dislocated when grinding disk B1 with a large grain size is replaced with grinding disk B2 with a fine grain size. Accordingly it is difficult to maintain the concentricity of electrode A. As a result, it takes a substantial period of time to grind and polish the tip to a mirror surface and furthermore, the form of the tip itself can change in an unintended way.
In view of the problems encountered in grinding the end portion of a welding electrode by grinding machines disclosed in the prior art which are; (1) when working with a grinding machine using a grinding disk with a large grain size and another with a fine grain size, it is troublesome to replace one grinding disk with another each time, and it is difficult to maintain the concentricity of the electrode when the grinding disks are changed, and (2) the use of two grinding machines is expensive and it is difficult to maintain the concentricity of the electrode; it is a general object of the present invention to provide a grinding machine for welding electrodes by which the end portion of even a very short electrode can be ground to a specific shape efficiently by a simple procedure and only the tip is finished to a mirror surface, i.e. all the grinding work can be done by this machine alone, and not using two grinding machines.
To solve the above-mentioned problems, a particular object of the present invention is to provide a grinding machine for welding electrodes the grinding machine comprising a box-like housing 1, a grinder motor 2 fixed within the housing 1, a disk-like grinding disk 3 fixed on a motor drive shaft 2a of a grinder motor 2 and provided with a grinding area 3A, a swing plate 4 provided on the housing 1 above the grinding disk 3 and supported movably in the direction of the axis xcfx86 of a motor drive shaft 2a, a cylindrical holder guide 6 tumably supported on the swing plate 4 in a vertical orientation with a downward portion protruding above the grinding disk 3 in the housing 1, an electrode holder 7 removably fitted into holder guide 6 and removably clamping an electrode A with its tip in contact with the grinding area 3A of the grinding disk 3, an electrode turning motor 8 fixed within the housing 1 to turn the holder guide 6 with the electrode holder 7 held therein, and a swing plate moving mechanism 9 for moving the swing plate 4 by a specific distance 1 along the axis xcfx86 of the motor drive shaft 2a. 
A further object of the invention is to provide a grinding machine as described above wherein the grinding area 3A of the grinding disk 3 is formed of a first grinding part 3a made of coarse grains and a second grinding part 3b made of fine grains.
According to the invention, the grinding disk exhibits several novel features. The grinding area 3A of the grinding disk 3 is formed ofxe2x80x94on a front side of the diskxe2x80x94a first grinding part 3a for grinding an end portion of the electrode A to form a cone andxe2x80x94on an outer circumferential side of the diskxe2x80x94a second grinding part 3b provided with a V-shaped grinding groove 3bxe2x80x2 for grinding a tip A0 of the electrode to a mirror surface.
The grinding area 3A of the grinding disk 3 is so constituted that the first grinding part 3a for forming the end portion of the electrode A in the form of a cone and the second grinding part 3b for polishing the tip A0 of the conically formed end portion of the electrode to a mirror surface are provided on the front side of the disk. The first grinding part 3a is on an inner portion of the disk in the radial direction and on the front side thereof in the thickness direction and the second grinding part 3b is provided on an outer portion of the disk in the radial direction and on said front side thereof but recessed in the thickness direction. The inclination angle xcex11 of a longitudinally inclined surface 3a1 defining the first grinding part 3a is the same as that of a longitudinally inclined surface 3b1, defining the second grinding part 3b, wherein the inclination angle xcex12 of a transversely inclined surface 3a2 defining the first grinding part 3a is the same as that of a transversely inclined surface 3b2 defining the second grinding part 3b, and the radius R of an arc-like joint between the longitudinally inclined surface 3a1 and the transversely inclined surface 3a2 of the first grinding part 3a is identical to that of an arc-like joint between a longitudinally inclined surface 3b1 and a transversely inclined surface 3b2 of the second grinding part 3b. The grinding area 3A of the grinding disk 3 is integrally formed of grains with a medium grain size.
The grinding area 3A of the grinding disk 3 comprises a longitudinally inclined surface 3a1 to form the end portion of the electrode A into the shape of a cone, a transversely inclined surface 3a2 to discharge grinding dust and a curved surface 3a3 to polish the tip A0 of the electrode A to a mirror surface.
The grinding area 3A of the grinding disk 3 is formed on both sides of a base of the grinding disk 3 symmetrically.
According to one feature of the invention, one end of the swing plate 4 is pivotably fixed on an upper wall of the housing (1) in such a way that the other end can be moved in the direction of the axis xcfx86 of the motor drive shaft 2a. 
According to a further feature of the invention, the electrode holder 7 comprises a cylindrical chuck guide 7a, a collet chuck 7b to be inserted into an end of the chuck guide and a cylindrical chuck screw 7c inserted into the chuck guide 7a from an upper side thereof, with the tip portion screwed into the collet chuck 7b. A spacer 16 with a specific thickness h may be placed on the chuck guide 7a so that the tip A0 of the electrode A is positioned within a grinding groove 3bxe2x80x2 of the second grinding part 3b. 
Another object of the invention is to provide a grinding machine as described above wherein the holder guide 6 with the electrode holder 7 held therein is turned by the electrode turning motor 8 via a round rubber belt 15.
A further object of the invention is to provide a grinding machine for welding electrodes as described above wherein the swing plate moving mechanism 9 comprises a moving handle 9a and a worm gear 9b which is turned by the moving handle and engages with a thread 4c provided on the swing plate 4.
Another object of the invention is to provide a grinding machine as described above wherein the distance for which the electrode holder 7 is moved by the swing plate moving mechanism 9 is indicated by a dial gauge 10 having a drive body 10a which is interlocked with a gauge stopper 4b provided on the swing plate 4.